Japanese examined patent publication No. H01-30896 “Noble Metal Extraction from Noble Metal-Containing Solution” discloses technology for recovering rhodium as rhodium black from ammonium hexachloro rhodate solution by adding formic acid to the solution.
However, it does not disclose a method for obtaining rhodium sponge from ammonium hexachloro rhodate solution in high yield.
The inventors have found out that rhodium sponge can be obtained in high yield without sacrificing impurity level by omitting the water-washing of rhodium black in a method for recovering rhodium sponge from ammonium hexachloro rhodate solution comprising reducing the rhodate with formic acid to obtain rhodium black and then calcining the rhodium black under hydrogen atmosphere.